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More accurately simulate the neutron flux profile#3653

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OceanNuclear wants to merge 127 commits intomainukaea/PROCESS:mainfrom

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Open

More accurately simulate the neutron flux profile#3653
OceanNuclear wants to merge 127 commits intomainfrom
neutronics

Commits

Commits on Mar 27, 2026

First commit - made a mockup of NeutronFluxProfile calculator.
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Added the effect of neutron multiplication, which is done by increasing the strength of the macroscopic (self and other) scattering matrix.
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relocated some functions
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Ruff improvements.
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Decided to implement a switch case for sinh(x/sqrt(-...))=-sin(x/sqrt(...)), instead of using complex number to cover both +ve and -ve sign in the sqrt.
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Some further progress on docstrings and equations.
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WIP - pushing to save progress.
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Transcribed the one-group constant (manually solved and verified by Desmos). Next step is to write the program for solving multi-group fluxes.
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Modified expression into sum-of-exponentials form, rather than sum-of-cosh+sinh.
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Added reaction rates calculations and neutron passage/escape flux.
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Added a unit test.
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Re-distributed where functions and classes live. Materials data related classes and functions are now in neutronics_data.
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Added publically available data (same source as openmc), so we don't have to import openmc.
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Made the decorator in neutronics.py follow the open-closed principle for ease of maintenace; added tests.
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made the four attributes: integration_constants, l_fw_2, l_bz_2, extended_boundary, to be self-populating dictionaries (populated by solve_group_n).
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Some quality-of-life things - _attempting_to_access attribute is made into a set, allowing index i to be discarded from it at every opportunity without having to check for membership.
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Keeping test updated.
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Corrected the ordering of the group structure to ensure that the first bin = highest energy/lowest lethargy.
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to cm fix.
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ruff fix
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Quality of life things: (clarify non-scattering into 'exclude elastic-scattering'.
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Allowed source macroscopic cross-section matrix to be larger than the total macroscopic cross-section (due to breeding)
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Added a property 'downscatter_only' which helps quickly determine if the transport problem is solvable without iterations.
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Clean up to make four separate dictionaries: micro_total_xs, micro_scattering_xs, micro_n2n_xs, micro_fiss_xs, to make the code more readable.
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Ruff fixes.
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Created the scattering matrix, and tested it. Next on the to-do list: n2n matrix.
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Added the n2n_matrix the feature, and added tests.
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Cleaned a bit up where the hypothetical 'integrate' function is used, to prep for its import
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Used numpy testing in appropriate places
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Ruff fix: numpy.random
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Docstring improvements
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Added plotting function.
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further improved the plotting.
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Formatting fix
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extended_boundary renamed to extended_boundary_cm
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Added regression test, and fixed all the little details to make the regression test work.
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regression test fix.
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Regression test added - conservation in total number of neutrons (they've either achieved 'removal' by reaction or escaped as neutron current.
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Added an IntegrationConstants class, which contains a validation method to make sure it's the right length.
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Made return None more explicit in some places.
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self.integration_constants conversion step 1 of 3: groupwise_neutron_flux conversion.
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Added d_fw and d_bz diffusion constants as attributes of NeutronFluxProfile.
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Fixed the ordering of the two arguments outputted by get_diffusion_coefficient_and_length
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self.integration_constants conversion step 2 of 3: solve_group_n conversion.
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self.integration_constants conversion step 3 of 3: neutron current and reaction rate conversion. Conversion is now complete.
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Fixed regression test
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Wrote up the solver for higher order groups, not tested yet.
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Handled events of same-characteristic-lengths more gracefully.
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Added validation to warn when there's elastic upscatter, or error when there's too much scattering cross-section, or warn when group structure bin edges reaching 0.
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ruff fixes.
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Separated the in_source matrix from the scattering matrix in MaterialMacroInfo.
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Turned the base functions from exp(x),exp(-x) to cosh(x),sinh(x); such that when the characteristic length goes imaginary, the function simply becomes cos(x),sin(x).
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Conversion from exponential basis to ((cosh/sinh)/(cos/sin)) bases complete.
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Fixed where the abs() are placed for taking the absolute value of x
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renamed the integration constants' working names to something a little more meaningful.
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One more regression test for now.
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Beginning removal of the _groupwise functions (because they don't need to be separated out like that)
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Minor change to the solve_n_group method to prep it for future (iterative) solver.
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Completed removal of the _groupwise functions.
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Completed one-group fission regression test.
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Updated the docs for MaterialMacroInfo parameters.
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Converted from cgs to metric
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Updated regression test to use cgs.
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Updated unit-test for checking the number of methods present.
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Pre-commit ruff fix
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Renamed the integration_constants to coefficients (because they're no longer obtained by integration)
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Removed unused constant
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Majority of the conversion from 2-layer model to the infinite-layer model is complete.
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Neutron flux and current are defined such that they're assumed to be unperturbed once the neutrons exit the final layer. I.e. the neutron flux and current at infinity == the neutron flux and curren…
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Updated docstring on Coefficients (now gives the correct use case) and populated the docstring of NeutronFluxProfile.
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Fixed the various off-by-one errors deliberately introduced a couple of commits ago (because I was in a hurry) in groupwise_neutron_current_through_interface
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Completed conversion from 2-layer model to infinite-layer model. Cleanup successful: unit test and regression test (1-group regression test case only) passed. Only the plotting function remains to …
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Added new class LayerSpecificGroupwiseConstants to encapsulate the behaviour of (NeutronFluxProfile.coefficients, NeutronFluxProfile.l2, NeutronFluxProfile.diffusion_const)
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Starting to fix plotting. Still need to verify that the layers' boundaries (i.e. interfaces) are properly drawn. Will need to make heating calculation method.
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Slight name change
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Finished updating the plotting function, so at the moment it works for both flux and current, but not for heating yet.
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Simplified the sign extraction function
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Implemented an attribute to record the neutron energy; and changed units from eV to Joule
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Updated documentation and test
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Slight fixes to docstring, and fix to regression test dummy energies so they're still valid under the new units (J, instead of eV)
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Docstring update for heating methods
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Added test to ensure integration of the heating term is done correctly.
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tested units output as well.
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Fixed the plot such that all discontinuity are minimized, and those discontinuity present are all justified (i.e. have physical meaning). This in turn updated the behaviour of some methods, and not…
OceanNuclear
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Does not allow higher energy bins than the incident neutron energy to exist without first re-writing solve_lowest_group
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Further modification to include a new attribute incident_neutron_group while keeping _calculate_mean_energy_and_incident_bin as a staticmethod.
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Removed conservation of neutrons condition entirely.
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Fix the list of conditions so it's no longer singular
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Bug fixes prompted by ruff
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Ruff fixes for tests too
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Fixed plotting zorder
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Prepared for the case that allows for contains_upscatter=True, where each NeutronFluxProfile.coefficient[:, n] will contain self.n_groups coefficients rather than n coefficients.
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Slightly tidied up the code that calculates the non-central cosh/sinh's coefficients (i.e. coefficients used to cancel the flux shapes contributed by other groups).
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Added placeholder list for summing up all of the skipped coefficients.
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slightly modified validate_length to allow for second+ passes to have coefficient length = total number of groups rather than the current group number.
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Put the cosh-sinh/cos-sin switching logic into dedicated methods, so the programmer won't have to write them out explicitly every time.
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Added feature to count the number of coefficient pairs.
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THe problem of deducing the next layer's coefficient given the previous layer can be written as an affine transformation in linear algebra (y = Ax+b). The method _get_propagation_matrix_and_offset_…
OceanNuclear
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Handling duplicate diffusion lengths is simpler than expected!
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Changed self.flux to self.fluxes, such that the incident neutron flux is recorded as a vector of Kronecka delta(n,g) * flux, where g is the group index matching the incident neutron energy.
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Changed the bounds of summation almost everywhere, and applied a shorthand to some summations (see _summation_shorthand) for ease of maintenance.
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Style cleanup and docstring update.
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unit tests passed, still need to fix regression tests
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Fixed the regression test too.
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Removed the print statements
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Added the 'solve()' method.
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Most tests have passed, but can't get conservation of flux to pass on multi-group multi-layer model. I suspect this has to do with the negative fluxes experienced by some models.
OceanNuclear
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Made the unit tests more comprehensive & passed on the Conservation of neutrons test
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Fixed the conservation of neutrons as well for regression test of neutronics.
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Ignored 'layer too narrow' warnings.
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Slightly improved the index-translation-table and cleaned up the error message, leaving the instructions on how to perform iteration calculations in the comments.
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Prepping neutronics_data.py for loading actual nuclear data.
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Modified the neutornics_data.py so that the MaterialsMacroInfo can be created without knowing the nuclear data first, *and then* knowing what isotopes' nculear data needs to be get, populate_from_n…
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Some ruff cleanups
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undid the try:import and sorted the remainder of the required_isotope_set when raising the RuntimeError for missing isotopes in the nuclear data library.
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Some ruff fixes
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Reordered methods to prepare for the addition of tritium breeding diagnostics
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Added tritium production rate getting methods, and added tests for them too.
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Moved the l2 and diffusion_coefficients into attributes of the neutronics_data.MaterialMacroInfo class.
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Fixes for regression tests to reduce the number of warnings, and ruff fixes.
OceanNuclear
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More ruff fixes
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Rebase
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No longer needs the .txt file
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Updated ruff fixes
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Ruff fix of json
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Commits on Mar 31, 2026

Fixed bug introduced because of ruff fixes.
OceanNuclear
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ruff formatting
OceanNuclear
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